The fungal cell wall polymer β-(1,3)-D-glucan is synthesized by the enzyme β-(1,3)-D-glucan synthase that is a complex composed of at least two proteins, Rho1p and Fks1p. Here, we report the nucleotide sequence of a single FKS gene and of the regulatory unit, RHO1 from the dematiaceous pathogenic fungus Alternaria infectoria. The predicted AiFks and AiRho share, respectively, 93% and 100% identity with that of Drechslera tritici-repentis. We also report that the sensitivity to caspofungin of eight different A. infectoria clinical strains is similar, with a MIC > 32 μg/ml and a MEC of 1 μg/ml, except for one strain which had a MEC of 1.4 μg/ml. This same strain exhibited one substitution at the hot spot 2, S1405A, compatible with less susceptible phenotypes, with the other seven strains having no mutations in either hot spot 1 or 2. The relative quantification of the expression of AiFKS and of AiRHO demonstrated a decrease in response to an exposure to caspofungin at 0.5 μg/ml.
Bibliographical noteThis study was partly supported by a Merck, Sharp & Dohme, Inc. Medical School Grant (P-1599) and by a funded project by FCT-Fundação para a Ciência e Tecnologia (PTDC/SAUESA/108636/2008; co-funded by COMPETE and FEDER).
JA was recipient of a pos-doc fellowship within the scope of MSD Medical School Grant (P-1599). CF is a recipient of a Pos-doc Fellowship from FCT-Fundação para a Ciência e Tecnologia (SFRH/BPD/63733/2009). BMAS is a recipient
of a research fellowship whithin the scope of the FCT Project PTDC/SAUESA/108636/2008.
The authors acknowledge Dr. Cameron Douglas, of Merck & Co., Inc., for providing protocols, and helpful and stimulating discussions.
Declaration of interest: The authors have no conflicts of interest. The authors alone are responsible for the content and writing of the paper.